Earthquake forecasting has the potential to save thousands of lives and billions of dollars in property damage. Accurate earthquake forecasting can give inhabitants of a pending earthquake area time to prepare and minimize the loss of life and property damage.
Unfortunately, the reliable forecasting of earthquakes has so far eluded scientists, as no one has yet developed an accurate system or method for determining when an earthquake will occur and how devastating it will be. Currently, one method of forecasting earthquakes uses statistics of recent earthquakes in a known earthquake region. The more recent an earthquake has occurred, the less likely another one will occur. Unfortunately, this method is a very inaccurate forecaster of earthquakes, because one cannot specify where or when an earthquake will happen. One can only determine that it is statistically more or less likely to happen in a region as time goes on. Further, this method is applicable only in zones where earthquakes have been observed before, because the method requires the use of past earthquakes in order to calculate future probabilities. To accurately and reliably forecast earthquakes, methods of forecasting are being considered that detect signals from impending earthquakes, rather than using data from those that have past.
One such method is searching for extremely low frequency (ELF) magnetic field fluctuations emitted from a zone where an earthquake is imminent. This method gained acceptance after the Oct. 17, 1989 Loma Prieta earthquake near San Francisco. A significant increase in the earth's ELF magnetic signal was measured by a ground based detector over a month before the Loma Prieta earthquake. Then, during the two weeks before the earthquake, there was an increase in background ELF magnetic signal, leading up to a large surge of ELF magnetic signal that occurred approximately three hours before the quake.
Further evidence that ELF magnetic activity is an accurate forecaster of earthquakes was obtained in both 1982 and 1989 by two different satellites that detected increased ELF magnetic signal before and after an earthquake occurred on earth. Two different satellites, a Russian satellite (Cosmos 1809) and a French satellite (Aureol 3), have detected ELF signatures at 140 -150 Hz while flying over earthquakes. Cosmos 1809 detected ELF signatures days to weeks after a M6+ earthquake and during the aftershock sequence at Spitak Armenia in 1989, while Aureol 3 detected ELF just prior to a M4.9 in April of 1982 in Saggadiera Japan. The position where the satellites observed the increased ELF magnetic signal correlated with the location of the actual earthquake. Unfortunately, these satellites were not specifically searching for ELF magnetic activity from earthquakes, and thus, a detailed analysis could not be done. These occurrences do, however, show promise for a space-based detector of ELF magnetic activity for earthquake forecasting.
Ground detectors used today are able to sense increased ELF magnetic signal when they are within approximately 20 miles of the epicenter of a pending earthquake. Using data from multiple detectors on the surface of the earth, one can try to determine the location of the largest increase in ELF magnetic signal in an earthquake area, which should correspond to the location of the earthquake. One can also try to use such data to determine the magnitude of an earthquake. It is hypothesized that the greater the ELF magnetic activity, the larger the earthquake will be. This hypothesis is consistent with a current theory as to why ELF magnetic measurements increase before an earthquake. The theory is that rocks begin to crack within the slip plane and thus tear electrons off of the lattices in the crystalline rock and create plasma. The plasma naturally emits electromagnetic waves, but it is only the ELF magnetic activity that is able to travel through the earth to the surface for detection. The severity of the earthquake and the increase in ELF magnetic signal depend on how much rock is cracked.
Both ground and space systems for detecting ELF magnetic precursors of earthquakes have significant drawbacks. First, ground systems can be extremely costly. Ground detectors are only able to measure the ELF activity within a certain distance from where they are placed. Because of the large area in which earthquakes can occur, numerous ground detectors are necessary to adequately cover an earthquake zone. In addition to the cost of the numerous detectors, one must factor in the cost for monitoring equipment and analysis and maintenance of the system. Due to the expense of ground systems, it is simply not practical to monitor or forecast earthquakes in areas with little historical risk from earthquakes, i.e., for a significant portion of the earth's landmass. However, devastating earthquakes may take place in areas that have not had earthquake activity for a long time or in areas that have not had a recorded earthquake. Thus, a better system is necessary in order to forecast or monitor earthquake activity in regions with little or no known earthquake activity.
Second, ground systems are often not practical for populated areas. The sensitive ground detectors are susceptible to problems with ELF magnetic noise. Various powered devices may create false positives for an ELF magnetic signal detector, making careful placement of the ground detectors to minimize outside influences essential. In highly populated areas, detectors may be intrusive, and it may not be possible to place detectors where they will not be susceptible to noise problems.
In order to maximize the area of detection and minimize noise, scientists have considered using satellites to detect ELF magnetic fluctuations from earthquakes. Satellites have the obvious advantage of being able to take measurements over a larger geographical region. However, the use of satellites has problems as well. First, satellite technology is extremely expensive to implement and maintain. An effective satellite monitoring system first requires the use of a satellite or group of satellites that have orbit(s) covering the areas of interest. Some scientists have attempted to use Global Positioning System (GPS) to monitor small geologic plate movements related to earthquakes. There is not, however, presently a satellite or system of satellites capable of detecting ELF magnetic fluctuations, which as discussed above, is a promising indicator of earthquakes. It is of great interest to society to implement such a system of satellites for monitoring ELF magnetic activity. Therefore, any savings in both the cost of production and the maintenance of the satellites is extremely valuable.
One issue that arises with the use of a satellite system is that each satellite is capable of detecting an ELF signal emanating from a single location on earth only once every 4 days. Therefore, satellites track ELF fluctuations periodically rather than continuously. It may take a few days for a satellite to verify that the ELF fluctuation measured is an earthquake precursor rather than an anomaly. This lag time in verification decreases the amount of time to prepare for the earthquake.
The present invention addresses the aforementioned problems with respect to cost, efficiency, and timeliness of earthquake forecasting.